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Half-life 3 (symbol t ½) is the time required for a quantity (of substance) to reduce to half of its initial value.The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable atoms survive.
This is a list of radioactive nuclides (sometimes also called isotopes), ordered by half-life from shortest to longest, in seconds, minutes, hours, days and years. Current methods make it difficult to measure half-lives between approximately 10 −19 and 10 −10 seconds.
Thirty-four artificial radioisotopes of tungsten have been characterized with mass numbers ranging from 156 to 194, the most stable of which are 181 W with a half-life of 121.2 days, 185 W with a half-life of 75.1 days, 188 W with a half-life of 69.4 days and 178 W with a half-life of 21.6 days.
A more intuitive characteristic of exponential decay for many people is the time required for the decaying quantity to fall to one half of its initial value. (If N(t) is discrete, then this is the median life-time rather than the mean life-time.) This time is called the half-life, and often denoted by the symbol t 1/2. The half-life can be ...
Tungsten (also called wolfram) [14] [15] is a chemical element; it has symbol W and atomic number 74. ... actually decays with a half life of 2.01 ...
and are the half-lives (inverses of reaction rates in the above equation modulo ln(2)) of the parent and daughter, respectively, and BR is the branching ratio. In transient equilibrium, the Bateman equation cannot be simplified by assuming the daughter's half-life is negligible compared to the parent's half-life.
In addition, there are 34 known synthetic radioisotopes, the most stable of which is 182 Hf with a half-life of 8.9 × 10 6 years. This extinct radionuclide is used in hafnium–tungsten dating to study the chronology of planetary differentiation. [5] No other radioisotope has a half-life over 1.87 years. Most isotopes have half-lives under 1 ...
As an extreme example, the half-life of the isotope bismuth-209 is 2.01 × 10 19 years. The isotopes in beta-decay stable isobars that are also stable with regards to double beta decay with mass number A = 5, A = 8, 143 ≤ A ≤ 155, 160 ≤ A ≤ 162, and A ≥ 165 are theorized to undergo alpha decay.